This specification for the instant application should be granted the priority date of Jun. 16, 2005, the filing date of the corresponding German patent application 10 2005 027 834.5.
The present invention relates to a torsional vibration dampener for dampening torsional vibrations of a rotationally driven shaft.
With rotationally driven shafts, e.g. the crankshafts of internal combustion engines, torsional vibrations often occur due to forces that act upon the shafts. The torsional vibrations cause great stress for the shaft and can, if they coincide with resonances of the shaft, even lead to breaking of the shaft. In order to cope with that it is common to provide torsional vibration dampeners, which, through the shifting of mass, dampen or eliminate the torsional vibrations. Two major groups of torsional vibration dampeners are thereby distinguishable, on the one hand so called resonant torsional vibration dampeners which, by means of elastic material deformation, essentially eliminate entirely the torsional vibrations that occur at certain speeds; on the other hand, torsional vibration dampeners that operate regardless of the speed and reduce torsional vibrations that occur via mechanical or fluidic friction and thus dampen it.
Resonant torsional vibration dampeners are known in various embodiments. A typical representative of that configuration is described for example in DE 588 245. A rubber ring is located, in a concentric manner, on the outer periphery of a hub that is connected to a crankshaft. A concentric outer ring that forms the vibrational mass is supported on the outer periphery of the rubber ring. The connection between the hub and the rubber ring on the one hand and between the rubber ring and the outer ring on the other hand is realized by means of friction fit, but can also be realized via other connection techniques such as vulcanizing or form fit. In torsional vibration dampeners of that kind, as mentioned above, the kinetic energy of certain torsional vibrations, for which the resonant torsional vibration dampener is adapted, is almost entirely eliminated through elastic material deformation. However, that means that resonant torsional vibration dampeners have practically no effect at other speeds than those for which they are adapted. A further problem is dissipating the heat that is released on account of the elastic material deformation.
Torsional vibration dampeners that operate according to the principle of hydraulic dampening regardless of the speed usually have a primary part that is fixedly attached to the shaft that is to be dampened and, arranged in a concentric manner in relation to the primary part, a secondary part that forms the vibrational mass and is pivotable—about a certain angle of rotation—around the common axis of rotation. Displacement chambers, arranged in a concentric manner in relation to the axis of rotation, are located between the primary and the secondary part. The displacement chambers communicate with each other via throttle or flow control locations. Relative movements between the primary and the secondary part change the volume of, in each case, two associated displacement chambers that are connected by means of a flow control location in such a way that the volume of the one displacement chamber decreases by the same amount that the volume of the other one increases. The displacement chambers are filled with a hydraulic fluid, so that in the case of a relative movement between the primary and the secondary part, due to the resulting change in volume of the displacement chambers, hydraulic fluid flows from the one displacement chamber through the flow control locations into the other displacement chamber. As a result of the fluidic friction in the flow control location, the system is deprived of kinetic energy via transformation into heat and hence, the system is dampened.
A torsional vibration dampener or a torsionally-elastic coupling of the aforementioned kind can be seen for example in DE 198 39 470 A1. Herein, spring elements for the transfer of the torque are provided between the primary and the secondary part. Associated with the displacement chambers is a fluid supply means with a feed pump, by means of which hydraulic fluid is pumped through supply channels into the displacement chambers. The hydraulic fluid flows back through backflow channels into a backflow chamber. The purpose of the fluid supply means is thereby to remove the air from the displacement chambers and to ensure that the displacement chambers, even prior to the start, are filled without enclosed air, so that at the time of the start the entire dampening capacity is available.
It is a disadvantage of torsional vibration dampeners operating on the basis of fluidic friction that they can dampen particularly pronounced torsional vibrations with large angles of shift or displacement, which occur for instance when passing through the resonance speeds of the shaft, only in an unsatisfactory manner.
Proceeding from the factual situation described above, it is an object of the present invention to configure a torsional vibration dampener, which, on the one hand, is effective over the entire speed range and, on the other hand, eliminates torsional vibrations with particularly large angles of shift or displacement. In a further development of the object, the torsional vibration dampener is to be configured in such a way that the heat that is released through the dampening can be dissipated easily and that an application on internal combustion engines used in vehicles is possible with little space being required.
The torsional vibration dampener of the present application comprises a hub that is adapted to be coaxially connected to the rotationally driven shaft relative to the axis of rotation thereof so as to rotate therewith, a rubber elastic ring connected to the hub, and a rotationally symmetrical body of inertia that is connected to the rubber elastic ring and acts as a vibrational mass. The body of inertia comprises a primary part and a secondary part, wherein the second part is coaxial relative to the primary part and is pivotable about a given angle relative to the primary part. Displacement chambers are formed by and are disposed between the primary part and the secondary part, wherein at least two of the displacement chambers communicate with one another via at least one flow control means. Relative movement between the primary part and the secondary part alters the volumes of each of the two displacement chambers that communicate with one another via the flow control means such that the volume of one of the displacement chambers decreases by the same amount by which the volume of the other displacement chamber increases. The displacement chambers are filled with a hydraulic fluid such that a fluid coupling is formed between the primary part and the secondary part. Upon a relative movement between the primary part and the secondary part, due to the resulting change in volume of the displacement chambers hydraulic fluid flows from the one displacement chamber into the other displacement chamber via the flow control means.
The torsional vibration dampener according to the invention is comprised of a resonant torsional vibration eliminator and a torsional vibration dampener and hence combines the advantages of both dampener types in one structural part. The torsional vibration dampener operates, regardless of the speed, according to the principle of hydraulic dampening and is practically applied onto the resonant torsional vibration eliminator. Furthermore, a torsional vibration dampener according to the invention does not require more space than a conventional torsional vibration dampener that operates according to one of the aforementioned principles. Moreover, it is advantageous that, in the case of resonance, the movements with relatively large angles of shift or displacement, which occur on the part between the hub and the vibrational mass that eliminates the resonant torsional vibrations, are additionally dampened by the hydraulically operating damper part.
Furthermore, since hydraulic fluid under pressure is supplied permanently to the displacement chambers, and since the excess hydraulic fluid is drained from the displacement chambers, an efficient removal of heat from the torsional vibration dampener is possible in an advantageous way.
An advantageous optimization of the configuration is provided in that the hydraulic fluid is supplied from the hub and the discharge flows back into the hub. Hence, the hydraulic fluid flows through the entire torsional vibration dampener, and consequently through the resonant torsional vibration dampener part as well, and the removal of heat is increased.
The inflow of the hydraulic fluid into the flow control location or means between two displacement chambers and the discharge of the redundant hydraulic fluid from the flow control location between two displacement chambers utilizes, in an advantageous way, the favorable pressure conditions in those locations and has the further advantage that for two displacement chambers only one inflow and one outflow opening is needed.
A simple and therefore advantageous arrangement of the configuration is accomplished by placing the intermediate parts in apertures in the primary part, since one aperture and one intermediate part, without a further expenditure, form two displacement chambers that are connected via throttle or flow control gaps. The advantageous configuration is supplemented in that the position of the intermediate parts is fixed relative to the primary part and relative to one another via the housing. In conjunction with the housing, the intermediate parts form the secondary part.
A particularly even and therefore advantageous inflow of the hydraulic fluid is realized in that the hydraulic fluid, coming from a distribution chamber in the hub, flows in a star-shaped, radial manner towards an annular chamber, which is located at the greatest possible distance from the hub. The return flow starts at the displacement chambers and leads, in a star-shaped, radial manner, to an annular discharge channel in the hub. Analogous points of the hydraulic circuit therefore have equal pressure conditions. Furthermore, the star-shaped, radial flow through the entire configuration causes an even and hence advantageous removal of heat from all parts of the torsional vibration dampener.
The first bores are configured as step nozzles, which lead from the annular chamber to the displacement chambers. That configuration essentially prevents, in an advantageous way, the backflow of the hydraulic fluid into the supply channels due to turbulences that are caused in the opening area of the corresponding step nozzle, so that back-pressure valves are unnecessary.
The ratio between the cross-sectional area of one of the first bores to the cross-sectional area of one of the outer flow control gaps and, respectively, the relation between the cross-sectional area of one of the second bores to the cross-sectional area of one of the inner flow control gaps lies in the range of 1:8 to 1:12. Consequently, in the case of a relative movement between the primary part and the secondary part, the transport of hydraulic fluid—in an advantageous way—occurs mainly through the flow control gaps. Hence, the backflow of hydraulic fluid into the supply channels or, respectively, the expulsion into the discharge channels is minimized and the dampening effect is maximized. On the other hand, the abovementioned dimensioning enables a sufficient and therefore advantageous quantity of flow of hydraulic fluid for the purpose of cooling the torsional vibration dampener.
Furthermore, it is particularly advantageous that in torsional vibration dampeners according to the invention that are installed on crankshafts of internal combustion engines, the lubricating oil from the lubricating circuit of the internal combustion engine can be used as the hydraulic fluid. A separate circuit for the hydraulic fluid is thus not necessary. The supply of the hydraulic fluid through a bore located in the rotationally driven shaft minimizes the expenditure in an advantageous way. Especially in internal combustion engines, the connection to the system of oil bores, which already exists in the crankshaft, can be realized via a simple connection bore.
A further advantage is that the hydraulic fluid flows out of the torsional vibration dampener through a bore in the rotationally driven shaft, e.g. the crankshaft of an internal combustion engine. The returning lubricating oil can hereby simply be led through the crankshaft to the oil pan that serves as the supply reservoir for the lubricating oil.